In some applications, such as gas turbine engine exhaust nozzles, certain components must be protected from the high temperature exhaust to prevent life reduction or failure of those components. In two-dimensional exhaust nozzles in particular, a cooling liner is typically mounted to each wall of the nozzle to prevent direct contact between the exhaust and the wall. Cooling air fed to the "cool side" of the liner may provide impingement cooling, convective cooling, or film cooling to maintain the temperature of the liner below the maximum allowable operating temperature of the liner material. The "hot side", or exhaust side of such liners may additionally be coated with a thermal barrier material to impede heat transfer to the liner, thereby greatly increasing the effectiveness of the liner. These coatings generally wear away with time, requiring the liner to be recoated or replaced.
Liner designs of the prior art include liners made of LAMILLOY.TM., a trademark of General Motors Corporation for a transpiration cooled liner material. One benefit of LAMILLOY.TM. is that it can be made of hard-to-form materials, such as mechanically alloyed iron based materials, which inherently provide high temperature durability. Liners made of LAMILLOY.TM. incorporate many small, straight, cooling air discharge holes which replenish the cooling film of the liner almost continuously. However, the straight cooling discharge hole configurations, to which LAMILLOY.TM. is limited, may not provide adequate cooling film effectiveness under certain nozzle operating conditions. Additionally, LAMILLOY.TM. cannot be coated effectively with thermal barrier material using current techniques, such as plasma (flame) spray coating, which tend to clog the discharge holes. Coating with a subsequent re-drilling of the holes has been tried with little success and high cost.
Other types of liners of the prior art incorporate concave discharge holes, or "bathtubs", formed into the hot side surface of the liner. Such liners are limited by manufacturing cost to "large bathtubs" and relatively large spacing therebetween. Although these liners provide effective film cooling under some conditions, the large spacing makes such liners susceptible to local cooling film migration induced by the exhaust local pressure gradients, which, in turn, reduces the local cooling effectiveness of the liner. In addition, the cost effective manufacture of these liners requires the use of very ductile materials.
What is needed is a nozzle cooling liner that is simple to manufacture, can be effectively coated with thermal barrier material, which replenishes the cooling film so often that it is less susceptible to local cooling film migration than the prior art, which gives the designer a wider choice of materials to use, and which allows optimization of both the hot side and cold side cooling.